Pressure actuated acoustic signal source

ABSTRACT

A bomb-type underwater signal source is disclosed having a detonating mechanism wherein the rupture of a shear disk assembly at a predetermined ocean depth permits the ambient hydrostatic pressure to compress the gas within a cavity and raise the temperature at one end of this cavity to a level sufficient to detonate first a confined secondary explosive positioned at this end of the cavity and then the main charge.

United States Patent Axelson et a1.

[451 June 27, 1972 Somerset, both of Mass; Elton Y. Mc- Gann,Williamsburg, Va.

[73] Assignee: The United States of America as represented by theSecretary of the Navy [22] Filed: Nov. 16, 1970 [21] App]. No.: 89,677

[52] U.S.Cl ..l02/10, 102/7, 102/16, 102/81 [51] Int. Cl ..F42b 21/00,F42b 22/36 [58] Field of Search ..l02/7, 10, 16, 81

[56] References Cited UNITED STATES PATENTS 3,391,639 7/1968 Bochman..102/7 Primary Examiner-Benjamin A. Borchelt Assistant Examiner.lamesM. Hanley Attorney-R. S. Sciascia and L. l. Shrago ABSTRACT A bomb-typeunderwater signal source is disclosed having a detonating mechanismwherein the rupture of a shear disk assembly at a predetermined oceandepth permits the ambient hydrostatic pressure to compress the gaswithin a cavity and raise the temperature at one end of this cavity to alevel sufficient to detonate first a confined secondary explosivepositioned at this end of the cavity and then the main charge.

5 Claims, 2 Drawing Figures PRESSURE ACTUATED ACOUSTIC SIGNAL SOURCE Theinvention described herein may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

The present invention relates generally to underwater acoustics signalsources and, more particularly, to an acoustic signal source whichutilizes only hydrostatic forces to detonate an explosive charge at apredetermined ocean depth.

In one common bomb-type underwater sound generator, hydrostaticpressures depress a plunger which contains a detonating charge and moveit into alignment with a firing pin. When these pressures reach apredetermined magnitude corresponding to a prescribed firing depth, ashear disk assembly is ruptured and a firing pin is driven into thealigned detonating charge. This charge is set off and so is theremainder of the in line explosive train consisting of the lead cup, thebooster and the main charge.

The safety feature in this type of sound signal source is provided bythe plunger which normally maintains the detonating charge in a safe outof line" position. This plunger can be depressed only after an armingsafety rod is withdrawn therefrom, either manually or by aerodynamicdrag forces acting on the bomb during the air drop portion of thedelivery. Furthermore, once armed, the bomb must reach a predeterminedwater depth sufficient to align the detonating charge with the explosivetrain. The many components required to achieve this degree of safety, aswell as those necessary for arming and firing the bomb, result in acomplicated and expensive device. Additionally, this complexityintroduces the problem of reliability of operation of the sound source.

It is accordingly a primary object of the present invention to provide asimplified arrangement for detonating an explosive charge in an oceanenvironment.

Another object of the present invention is to provide a detonator whichis inexpensive, compact, safe and highly reliable and which operates atrelatively high, hydrostatic pressures.

Another object of the present invention is to provide a detonator for anexplosive charge which utilizes hydrostatic pressures to increase thetemperature at the explosive charge to a level sufficient to cause itsdetonation.

Another object of the present invention is to provide a bomb-typeunderwater signal source which cannot be accidentally detonated on thesurface or in relatively shallow water but which requires substantialhydrostatic pressures for its operation.

Another object of the present invention is to provide a detonator forunderwater explosives which eliminates the need of all sensitiveinitiators and the need for an out of line" safety feature and an inline" explosive train.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic drawing showing the complete structure of abomb-type acoustic signal generator utilizing the principle of operationof the present invention; and

FIG. 2. is a simplified drawing of a detonator which can be used invarious explosive devices.

Briefly and in somewhat general terms, the above objects of inventionare accomplished according to the present invention by utilizing therupture of the shear disk assembly at a preselected ocean depth as ameans for permitting the ambient hydrostatic pressures to compress thegas within a cavity and raise the temperature within this cavity to alevel sufiicient to detonate a confined secondary explosive elementwhich is positioned at the other end of the cavity. When the seawaterrushes into the air cavity, the compression of the air therein which isin contact with the secondary explosive occurs sufficiently fast so asto be adiabatic and create a peak air temperature to cause deflagration.This defiagration, together with its instantaneous pressure rise andwith a proper confinement of the explosive, results in the detonation ofa secondary explosive column.

Referring now to FIG. 1 of the drawings, it will be seen that thebomb-type, underwater acoustic signal source includes a nose section Iwhich houses a shear disk assembly 2 that is seated in place by atensioningnut 3 against the back wall portion 4 of an inner centralchamber 5.

A plurality of radial apertures, such as 6 and 7, are cut through thenose section to communicate with inner chamber 5. Likewise, suitableapertures, such as 8 and 9, are cut through a body portion of thetensioning nut 3 to communicate with a central bore 10 formed in one endof this nut. This arrangement of openings allows one face of the sheardisk assembly 2 to be exposed to the ambient sea pressure when the soundsignal source is immersed in the ocean.

Also communicating with inner chamber 5 and the back wall portion 4thereof is a conical cavity 1 l, the base of which commences at thiswall. The base of the cavity is effectively sealed off by the shear diskassembly so that the air contained therein is normally maintained atatmospheric pressure. The

apex of cavity 11 extends into one end of an explosive container 12which has a circular flange that locks behind a backing plate 14 that isbolted or otherwise attached to the rear of nose section I. Containedwithin the explosive charge holder 12 in a central bore is the secondaryexplosive charge 13. A portion 16 of this charge serves to close theotherwise opened end of the apex of cavity 11. The secondary charge 13is held in place by a spring cap 15 which clips over a reduced diameterend portion of the explosive container, forcing this charge to the left,as shown in the figure, so as to have it abut the apex of the cavity.

It would be pointed out that the shear disk assembly 2, together withthe conical cavity 11, the secondary explosive container 12 and thesecondary explosive column 13, constitute the detonating mechanism ofthe bomb-type signal source. This subassembly, that is, the nose sectionI with the explosive container 12 attached thereto and with thesecondary explosive column 13 locked in place by spring cap 15, may bereadily connected to any explosive device for detonation thereof at apredetermined ocean depth.

In the present case, the main explosive charge 17, which is of a plasticcomposition, is contained within a midsection 18 of the bomb andsubstantially fills the complete interior thereof except for the centralcut-out section into which fits the secondary explosive container 12.The tail section of the bomb is filled with sponge rubber l9, and thisrubber acts as a spring to compress the plastic explosive and keep itfirmly abutted against the end cap 15 associated with the secondaryexplosive charge holder 12. The midsection and tail section of the bombmay be made of unitary construction, and a portion of the exteriorcasing 20 may be fabricated with an inner directed rim which snaps intoa circumferential slot 21 formed in nose section I.

lt will be appreciated that the only explosive in the detonatingmechanism is the secondary explosive column I3 and that there are nomoving parts to this mechanism.

It will also be appreciated that the apparatus as described may besafely handled without any danger of its premature ignition since thetemperature within the air cavity will be much below the level needed toignite the secondary explosive column.

When the assembled apparatus, as shown in FIG. 1, is launched from anaircraft or dropped at the ocean surface, it falls within the ocean withseawater entering the nose portion through the various apertures, andthe ambient ocean pressure acting against shear disk assembly 2. The airwithin cavity 1 1 remains at atmospheric pressure because of the barrierpresented by this disk assembly. When the bomb reaches its preset depthas determined by the design of the disk assembly, the disk shears andseawater, because of the relatively great ambient hydrostatic pressure,rushes into the conical cavity. The converging walls direct this flowinwardly and the water, acting as a piston, causes the air within thecavity to be compressed into the apex. The compression of this airoccurs fast enough to be essentially adiabatic. The magnitude of thiscompression at the depths involved is enough to create a peak airtemperature in contact with the secondary explosive column 13 to causedeflagration. This deflagration and the confined condition of thesecondary explosive column results in a transition from defiagration todetonation first of this column and then of the main explosive 17.

It can be shown by a mathematical analysis that if the final volume ofthe cavity is small compared to the original size of the cavity, thenthe increase in temperature, A! C. is equal approximately to 3.33 h,where h is the water depth at which the disk assembly is ruptured. Thus,for example, at a hundred feet, the temperature rise is 330.33 C., at1,000 feet, 3,303.33 C. and at 10,000 feet 33,030.27 C. Likewise, it canbe shown that the cavity need not have the conical shape shown in FIG. 1but may be, for example, of cylindrical geometry.

One of the advantages of the arrangement hereinabove described is thatthe secondary explosive material is kept stationary and in a line withthe main explosive charge at all times. The acoustic signal apparatus,since it needs no safety wire or other safety retaining device, is thusalways ready for immediate use, a characteristic which is highlydesirable in a combat or emergency situation.

In FIG. 2 there is disclosed the general details of the detonator whichemploys the operating principle of the present invention and which maybe utilized to detonate a lead cup normally used with any explosivetrain. The apparatus consists of a secondary explosive charge holder 30which, like its counterpart 12 in FIG. 1, has a central conical cavity31 whose apex portion communicates with a longitudinal bore that contains the secondary explosive column 32. A shear disk assembly 33 againcloses ofi the circular base portion of conical cavity 31 andeffectively entraps the air therein and maintains it at atmosphericpressure. A retaining cap 34 is screwed onto a reduced diameter endportion of the charge holder and serves to maintain the shear diskassembly in place. Formed in the head of the retaining cap is a centralopening 35 which permits the ambient sea pressure to act on one face ofthe shear disk assembly.

In this particular modification, the explosive lead cup 41 fits into arecess in the rear of a plug 40 which is screwed into the base ofcharger holder 30. The explosive element 42 of this lead cup ismaintained in alignment with an air passageway 43 cut through plug 40which communicates with the secondary explosive column 32. An aluminumdisk 44 is introduced behind plug 40 so as to block this air passagewayand support the exploding column 32.

The rupture of the shear disk assembly at the preset depth again causesthe temperature at the face of the secondary explosive column toincrease to a level sufficient to cause detonation of this column. Whenthis occurs, hot metal particles from aluminum disk 44, as well as theshock waves from the explosion, travel through passageway 43 anddetonate the explosive lead cup 41. Detonation of this cup, of course,results in the subsequent detonation of any main explosive charge whichis butted up against its output end.

In this modification, the detonator is positioned within a casing 50 andthe main explosive charge occupies compartment 51 thereof.

The booster material in the usual underwater sound signal weighsapproximately 31 grams. in the detonator above described, no suchbooster is required, and the explosive loaded pickup cup weighs only 3grains. Total explosive weight of the assembled detonator is less than 1gram.

Since the detonator of FIG. 2 has no moving parts, its reliability is ofa high order. Likewise, its storage life is prolonged and little or nomaintenance is required during the storage.

What is claimed is:

1. Apparatus for detonating an explosive charge at a predetermined depthcomprising, in combination,

a member having a cavity formed therein which is open at both endsthereof;

a shear disk assembly closing one end of said cavity; an explosivecharge confined within said member such that a portion of said chargecloses the other end of said cavity; and

said shear disk assembly rupturing at said predetermined ocean depth andthereby allowing water to rush into said cavity, compress the gaspresent therein and raise the temperature thereof to a level sufficientto detonate said explosive charge.

2. In an arrangement as defined in claim 1,

wherein said cavity has a conical shape; and

wherein said shear disk assembly is positioned at the base and saidexplosive charge at the apex of said conical shape.

3. Apparatus for detonating an explosive charge at a predetermined oceandepth comprising, in combination,

an explosive charge holder having a cavity formed therein which is openat one end thereof and having a compartment which is in communicationwith the other end of said cavity;

an explosive charge confined within said compartment and effectivelyclosing one end of said cavity; and

a shear disk positioned against the other end of said cavity and closingthis end of said cavity; said shear disk maintaining the gas presentwithin the interior of said cavity at atmospheric pressure until saidshear disk assembly is ruptured at said predetermined ocean depth,whereupon water rushing into said cavity from said other end thereofcompresses the gas present therein and raises the temperature thereof toa level sufficient to detonate said explosive charge.

4. In a bombdype underwater acoustic signal source, the combination ofan explosive charge holder having a cavity formed therein which is openat opposite ends thereof;

a shear disk positioned against one end of said cavity and closing thisend of said cavity, said shear disk being arranged so as to rupture at apredetermined hydrostatic pressure when said bombtype acoustic signalsource is immersed in a fluid medium;

a secondary explosive charge confined within said explosive chargeholder such that a portion thereof serves as a closure means for theother end of said cavity, whereby the gas present within said cavity ismaintained at atmospheric pressure until said shear disk is ruptured;

a metallic disk contacting an end portion of said secondary explosivecharge which is remote from that portion which serves as said closuremeans;

a cap attached to said explosive charge holder and maintaining saidmetallic disk in place, said cap having a passageway formedtherethrough; and

a main explosive charge positioned against said cap whereby, when saidshear disk is ruptured, water rushing into said cavity compresses thegas present therein and raises the temperature thereof to a levelsufficient to detonate said secondary explosive charge and sendparticles from said metallic disk and shock waves through saidpassageway to denote said main explosive charge.

5. In an arrangement as defined in claim 4 wherein said cavity has aconical shape with said shear disk positioned at the base and saidsecondary explosive charge at the apex thereof.

1. Apparatus for detonating an explosive charge at a predetermined depth comprising, in combination, a member having a cavity formed therein which is open at both ends thereof; a shear disk assembly closing one end of said cavity; an explosive charge confined within said member such that a portion of said charge closes the other end of said cavity; and said shear disk assembly rupturing at said predetermined ocean depth and thereby allowing water to rush into said cavity, compress the gas present therein and raise the temperature thereof to a level sufficient to detonate said explosive charge.
 2. In an arrangement as defined in claim 1, wherein said cavity has a conical shape; and wherein said shear disk assembly is positioned at the base and said explosive charge at the apex of said conical shape.
 3. Apparatus for detonating an explosive charge at a predetermined ocean depth comprising, in combination, an explosive charge holder having a cavity formed therein which is open at one end thereof and having a compartment which is in communication with the other end of said cavity; an explosive charge confined within said compartment and effectively closing one end of said cavity; and a shear disk positioned against the other end of said cavity and closing this end of said cavity; said shear disk maintaining the gas present within the interior of said cavity at atmospheric pressure until said shear disk assembly is ruptured at said predetermined ocean depth, whereupon water rushing into said cavity from said other end thereof compresses the gas present therein and raises the temperature thereof to a level sufficient to detonate said explosive charge.
 4. In a bomb-type underwater acoustic signal source, the combination of an explosive charge holder having a cavity formed therein which is open at opposite ends thereof; a shear disk positioned against one end of said cavity and closing this end of said cavity, said shear disk being arranged so as to rupture at a predetermined hydrostatic pressure when said bomb-type acoustic signal source is immersed in a fluid medium; a secondary explosive charge confined within said explosive charge holder such that a portion thereof serves as a closure means for the other end of said cavity, whereby the gas present within said cavity is maintained at atmospheric pressure until said shear disk is ruptured; a metallic disk contacting an end portion of said secondary explosive chArge which is remote from that portion which serves as said closure means; a cap attached to said explosive charge holder and maintaining said metallic disk in place, said cap having a passageway formed therethrough; and a main explosive charge positioned against said cap whereby, when said shear disk is ruptured, water rushing into said cavity compresses the gas present therein and raises the temperature thereof to a level sufficient to detonate said secondary explosive charge and send particles from said metallic disk and shock waves through said passageway to denote said main explosive charge.
 5. In an arrangement as defined in claim 4 wherein said cavity has a conical shape with said shear disk positioned at the base and said secondary explosive charge at the apex thereof. 